A useful criteria for determing when a distribution is determined by its moments is that it admits a moment generating function [1]}. Suppose that the distribution of a random variable \(W\)  is determined by its moments. The method of moments [1]} ensures that \(W_n(\lambda )\)  converges in distribution to \(W\)  provided \(W_n(\lambda )\)  has moments of all orders and for all \(j\ge 1\) ,
\(\lim _{n\rightarrow \infty } \mathbb {E}\big [W_n(\lambda )\big ]^j=\mathbb {E}[W^j].\) 
